Air filter system and filter element

ABSTRACT

An air filter system ( 30 ) includes a filter housing ( 10 ) with a filter element ( 1 ) received within the housing. A secondary housing is secured to and closing the filter housing. The secondary housing includes a locking element operable to engage the filter housing and the filter element. The filter element ( 1 ) includes at least one fastening element ( 7 ) wherein the locking element ( 22 ) of the secondary housing ( 20 ) engages the at least one fastening element ( 7 ) in such a way, when the filter element ( 1 ) is accommodated in the filter housing ( 10 ) and is disposed between the filter housing ( 10 ) and the secondary housing ( 20 ), that the secondary housing ( 20 ) is detachably clamped to the filter housing ( 10 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is bypass continuation of international patentapplication no. PCT/EP2012/052696, filed Feb. 16, 2012 designating theUnited States of America, the entire disclosure of which is incorporatedherein by reference. Priority is claimed through PCT/EP2012/052696 toGerman patent application no. 10 2011 011 595.1, filed Feb. 17, 2011.

TECHNICAL FIELD

The present invention relates to an air filter system and a filterelement for an air filter system, in particular for a multi-stage airfilter with cyclone precleaner.

BACKGROUND ART

Cyclone separator, also called centrifugal force separator, cyclone orcyclone filter, are used to separate solid or liquid particles containedin gases.

In the cyclone separator, gases together with the particles are set intoa rotating movement by a corresponding constructive design. Thecentrifugal forces acting on the particles accelerate them radiallyoutwards. As a result, they are separated from the gas flow, which isguided inwardly and discharged.

Due to the moderate filtration performance with very fine particlescompared with other methods, the cyclone filtration is often used aspart of a filter chain in a multi-stage air filter system. Forseparating fine dust particles it is, therefore, state-of-the-art toequip the cyclone filter additionally with a conventional final filter.The air pre-cleaned by the cyclone filtration is conveyed through thefilter medium of the final filter, wherein impurities of the air aredeposited on the filter medium. By so doing, it is possible to enhancethe filtration performance of the cyclone filter.

The state-of-the-art filter elements are in some cases onlyinsufficiently adapted to cope with the special requirements for beingused as final filter in an air filtering in a cyclone filter downstreamof the cyclone filtration. One problem, in particular, is that the airis swirled after the cyclone filtration. As a result, the filter mediumof the final filter is flowed through irregularly, thus reducing thefiltering effect.

Furthermore, conventional state-of-the-art filter elements are commonlyequipped with filter media having cross-sections in even, round or ovalshape. If a filter medium is now provided with an optimizedcross-section shape for achieving an enhanced filtration performance, aparticularly high degree of air purity can be achieved with the airexiting the filter.

Technical systems, consisting for example of an internal combustionengine and the upstream air filter for cleaning the inlet air to thecombustion chamber of the internal combustion engine, are oftendeveloped as an overall system. As a consequence, specific requirementsfor the maximum mounting space, the accessibility for changing thefilter element, the pressure loss in the system and the degree of purityof the air supplied to the internal combustion engine and therefore alsoto the filtration performance of the upstream air filter result fromthis.

Furthermore, single- and multi-stage filter systems, in particular witha cyclone precleaner, often have, for example, the disadvantage thatchanging the filter elements requires more effort because of themounting space conditions.

DISCLOSURE OF THE INVENTION

It is therefore the objective of the present invention to provide anenhanced air filter housing, an enhanced air filter element and anenhanced air filter system, in particular for a multi-stage filtersystem with cyclone precleaner, which in particular allow astraightforward and/or reliable assembly and in particular an optimizedflow.

This objective is accomplished by an air filter system with thecharacteristics of claims.

A corresponding filter housing such as, for example for an or with anintegrated cyclone precleaner, is configured for an inner accommodationand locking of a filter element, the filter element featuring at leastone fastening element, to which, when the filter element is accommodatedin the filter housing and disposed between the filter housing and asecondary housing, a locking element each of the secondary housing canengage such that the secondary housing can be clamped to the filterhousing.

A clamping of the filter housing and the secondary housing and thus thelocking of the filter element between the filter housing and thesecondary housing is realized by means of the fastening element of thefilter element. If the filter element does not feature a correspondingfastening element, because for example a third-party filter element isinserted, a clamping of the secondary housing to the filter housing isnot possible. This ensures that only filter elements can be used, whichfeature the corresponding fastening element. It is furthermore ensuredthat the filter housing cannot be closed without a filter element beinginstalled. As a result, in particular an operating error which can leadto an operation without filter element and therefore to damages of theinternal combustion engine, is avoided.

As secondary housing can particularly be conceived: cover plates, intakegrilles, cyclone blocks, cyclone precleaners (blocks) and/or housingcovers, in particular with inlets and outlets.

In embodiments, the filter element is completely accommodated by thefilter housing. The filter housing encloses for example the volume ofthe filter element. It is possible that the filter housing or acorresponding filter assembly, which comprises the filter housing, thefilter element and the secondary housing, is designed in such a way thatthe fastening element and the locking element allow a clamping of thefilter element between the filter housing and the secondary housing onlyif it is completely accommodated in the filter housing.

To realize this, the fastening element is preferably designed asprotrusion that extends through a hole on the filter housing andprotrudes beyond it, when the filter element is assembled with thefilter housing in such a way that the filter element is, preferablycompletely, accommodated in the filter housing. The locking elements onthe secondary housing are preferably designed as fixing elements, whichare locked or caught with the associated fastening element.

By protruding through the filter housing, the fastening elements createcontact points, with which the locking elements can be locked. If thefilter element is inserted into a filter housing that does not featurethe corresponding protrusions, a locking by means of the lockingelements will not be possible, so that the insertion of incorrect filterelements and thus a deterioration of the filtration performance isavoided. The fastening elements preferably protrude through the holestowards the filter housing in the direction in which the filter elementcan be installed or inserted into the housing, i.e. in mountingdirection. Furthermore, the fastening elements preferably protrudethrough the holes outside of a sealing of the filter element. The holesare therefore preferably disposed outside of the interior space of thefilter housing in which the filter element can be accommodated, and thusin particular also outside of the sealing surface of the filter housing.

According to a preferred embodiment, the locking elements have ahook-shaped design and engage behind the respective fastening element orinto the recess or undercut at the respective fastening element. As aresult, a locked form-fit and/or force-fit connection is created. As aresult, the connection of filter housing and secondary housing can beeasily and quickly disconnected and realized without additional tools. Aquick and straightforward change of the filter element is possible.

The locking elements on the secondary housing are preferably at leastpartially resilient and particularly preferred designed as metal clampsor brackets. As a result, the locking elements can be easily snapped inplace behind the fastening elements by resiliently deforming them duringthe snap-in process or during clamping of the filter housing to thefilter element and the secondary housing. As a result, an additionalresilient bearing of the locking elements can be avoided.

According to a preferred embodiment, the holes on the filter housing aredisposed on the side facing away from the filter element on inclinedfilter housing sections which extend under an angle between 45 and 90degrees in relation to the longitudinal extension direction of therespective associated hole. As a result, it is possible that the lockingelement on the filter housing, namely on the inclined filter housingsections, slides downwards, if no protrusions of the filter elementproject from the holes in the filter housing, i.e. if no filter elementwith the protrusions is inserted. In this case, the inclined filterhousing sections allow a reliable sliding of the locking elements on thefilter housing.

According to a preferred embodiment, the filter housing features innerribs, which extend in installation direction of the filter element alongthe filter element. These ribs extend preferably in the installationdirection of the filter element. An accommodated filter element extendsthen by abutting on the ribs. For example, the totality of the ribsextending inwardly reproduces an outer cross-sectional contour of thefilter element. Using the ribs avoids using an inappropriate filtermedium, that makes it necessary to sealingly contact the interior sideof the filter housing. This will ensure that the inflow space can bekept in the preferred size when using replacement filter elements.

According to a preferred embodiment, the filter housing features an ovalinner housing cross-section shape. The filter element can also have anoval, however also a kidney-shaped or octagon-shaped cross-sectionshape. As a result, the use of filter elements that are not compatiblecan be made particularly difficult.

According to a preferred embodiment, a sealing plate is disposed betweenfilter housing and filter element. Furthermore, this features preferablyprotrusions, which engage in recesses on the filter housing or into theholes. By this measure, a correct positional orientation of the sealingplate is forced in order to achieve a reliable sealing of filter housingand filter element. The sealing plate is, for example, part of thefilter element. The sealing plate is preferably disposed on an end diskor end plate of the filter element or designed as one of these. Theshape of the sealing plate is preferably adapted to the shape of the twoadjacent housing components, which means to the filter housing and thesecondary housing.

The sealing plate is preferably provided with an annular sealing, whichcan be sealingly brought into engagement with a corresponding sealingarea of the filter housing. The sealing plate and the associated sealingsurface of the filter housing are preferably designed on one narrow sideessentially rectangular (in this case, the angles can be rounded), andon the other narrow side in the shape of a semicircle or half of anellipsis. As a result, a correctly positioned mounting of the filterelement can be ensured. Preferably, the annular sealing for sealing thefilter element in the filter housing extends along this shape. This isparticularly advantageous for a precise signal of the air-flow meter,for it can be ensured that irregularities in the filter elementstructure are always disposed at the same location in the housing. Theseirregularities can, for example, be the connection point of an annularlyclosed folded filter bellows or the initial or end points of asemi-finished filter material with alternately closed ducts wound inparticular onto a core.

In one embodiment, a filter element, comprising a star-shaped folded,annular, in particular circular ring-shaped closed filter bellows madeof a filter medium such as, for example, fleece or cellulose or acombination thereof as well as a corresponding filter housing for afilter system, is provided. The filter element features at the top end asealing, in particular round end disk, which sealingly closes a frontface of the filter element and thus separates the raw side outside ofthe filter element from the clean side in the filter element interiorspace. The end disk features in particular several fastening elements,e.g. in the shape of protrusions or buttstraps, which can be inparticular disposed at an annular extension of the end disk, which are,for example, connected with the inner area of the end disk, whichencloses the frontal end of the filter element by means of star-shapeddisposed distance ribs or a distance ring.

In an embodiment of the filter housing corresponding to the filterelement, preferably openings or holes are disposed into which can engagethe protrusions of the filter element. Once the filter element isaccommodated in the filter housing, the protrusions engage preferablyinto the holes. In this case, the protrusions in the area of the holesare so long that they protrude from the holes of the filter housing. Theopenings are preferably provided outside of the filter housing interiorspace and do not create an access to the interior space of the airfilter. In this case, the filter element is disposed particularly withits end disk between the filter housing and a secondary housing designedas housing cover.

In one embodiment, locking elements, which are for example attached tothe secondary housing in the form of wire clamps or engaging members,can then engage into the protrusions where they protrude from the filterhousing, so that the filter element can then be clamped between thesecondary housing and the filter housing. Several locking elements andcorresponding protrusions and openings are preferably provided which arepreferably evenly distributed across the circumference of the inparticular circular end disk. Preferably 2-6, particularly preferred 3-5locking elements are provided.

In one embodiment, the end disk of the filter element is disposedbetween the secondary housing and the filter housing, wherein the enddisk is clamped between the two components when the locking elementsengage behind the protrusions.

In one embodiment, the protrusions are provided for engaging through theopenings on the filter housing and prevent also a rotating movement ofthe filter element in the filter housing when they are in the engagementposition. As a result, a rotation of the filter element in operation andthus an undesired modification of the air-flow meter signal can beprevented

Further embodiments of the invention are subject of the subclaims aswell as of the examples of an embodiment of the invention described inthe following. Furthermore, the invention is explained in detail basedon examples of an embodiment with reference to the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

It is shown in:

FIG. 1: a schematic perspective exploded view of an air filter with afilter housing and filter element according to a first example of anembodiment;

FIG. 1A: an alternative embodiment of the example of an embodimentaccording to FIG. 1;

FIG. 2: a schematic perspective representation of the air filter inmounted state according to the first example of an embodiment;

FIG. 3-5: schematic perspective sectional representations of the airfilter according to the first example of an embodiment;

FIG. 6: a perspective representation of a filter housing;

FIGS. 7 and 8: top views of examples of an embodiment of the filterhousing and filter element;

FIGS. 9 and 9A schematic perspective representations of a furtherexample of an embodiment of an air filter;

FIGS. 10 and 10A schematic perspective sectional representations of theexample of an embodiment shown in FIGS. 9 and 9A;

In the figures, the same reference numerals denote identical or analogcomponents, unless otherwise stated.

DETAILED DESCRIPTION

FIG. 1 shows a schematic perspective exploded view of an air filter 30with a filter housing 10 and filter element 1 according to a firstexample of an embodiment. FIG. 2 shows the air filter 30 in an assembledstate. In the orientation of FIGS. 1 and 2, the air to be cleaned flowsfrom the right to an inlet 3, flows through the multi-stage filterchain, which is called air filter 30, and exits from an outlet 4 at theleft in cleaned condition. The cyclone separation is carried out by anassembly consisting of a cyclone upper section, which is calledsecondary housing 20 in the following, and a cyclone bottom section 33.Several immersion tubes 36, which cooperate with individual centrifugalforce separators 35 on the secondary housing 20, can be recognized atthe cyclone bottom section 33. The cyclone bottom section 33 is held bymeans of a fastening element, for example a screw 34, at the cycloneupper section or secondary housing 20.

Raw air is supplied at the inlet 3 into the air filter 30 on the side ofthe cyclone upper section 20. The cyclone separation removes coarseparticles from the air, which are collected in the bottom section of thesecondary housing 20. A particle removal opening 5, which is closed by avalve 6, is provided. The accumulated particles can be removed inpredefined maintenance intervals, however, the valve can also be openedmanually.

The air is then guided through the filter medium 2 of the filter element1 represented in the figure to the left of the cyclone bottom section 33to carry out a further filtration of particles, in particular of fineparticles. A further filter element is provided downstream as secondaryelement 32. The air is additionally filtered by means of the secondaryelement 32 and exits at the outlet 4 of the filter housing 10 asfiltered air.

The filter element 1 features at the top end a sealing end disk 8, whichhas several fastening elements 7 in the shape of protrusions orbuttstraps. Openings or holes 12 are disposed in receptacles on thefilter housing 10, into which can engage the protrusions 7. Once thefilter element 1 is accommodated in the filter housing 10, that means ifthey are in FIG. 1 completely telescoped essentially in horizontaldirection, the protrusions 7 engage into the holes 12. In this case, theprotrusions 7 in the area of the holes 12 are so long that they protrudein the orientation of FIG. 1 in the picture to the left from the holes12 of the filter housing 10. The openings 12 are provided outside of thefilter housing 10 and do not create an access to the interior space ofthe air filter 30. In this case, the filter element 1 is disposedparticularly with its end disk 8 between the filter housing 10 and thesecondary housing 20.

Locking elements 22, which are attached to the secondary housing 20 inthe form of wire clamps in this example of an embodiment, can thenengage into the protrusions 7 where they protrude from the filterhousing 10, so that the filter element 1 can then be clamped between thesecondary housing 20 and the filter housing 10.

FIG. 1A shows an embodiment derived from that in FIG. 1 in which thesecondary housing 20 is shown as housing cover with inlet port, whereinthe housing cover is also provided with locking elements 22.

FIGS. 3-5 show schematic perspective sectional representations of afilter housing 10 and secondary housing 20 with accommodated filterelement 1 according to the example of an embodiment in FIG. 1. In theorientation of FIGS. 3-5 at the top is represented the secondary housing20 with the (hidden) cyclone separators and below the filter housing 10.Between the secondary housing 20 and the filter housing 10 are disposedthe cyclone bottom section 33 and the end disk 8 of the filter element1. From the filter element 1 or the end plate 8 protrusions 7 can berecognized, for the filter element 1 is accommodated in the filterhousing 10. It can be seen in FIG. 3 that protrusions 7 are, on the onehand, provided for being inserted through the holes 12 on the filterhousing 10, and that, on the other hand, further protrusions 17 areprovided. The protrusions 7 extend through the openings 12 in the filterhousing 10. For the further protrusions 17, there are no associatedopenings on the filter housing 10 on the right side in the orientationof FIG. 3. On the other hand, blocking ribs 27 are provided on theexterior side of the filter housing 10, which prevent the filter element1 from moving downwards. In case the mounting orientation is not used asintended, the filter element 1 can not be accommodated completely in thehousing 10. This ensures that the sealing end disk 8 is accuratelyplaced onto the edge 40 of the filter housing 10 and that it can closefluid-tightly.

FIGS. 4 and 5 show the assembly according to the intended use of thefilter element 1 and the housing components 10, 20. The locking element22 attached to the secondary housing 20, which is realized in thisexample of an embodiment as wire clamp or bracket, clamps the secondaryhousing 20 and in particular the cyclone bottom section 33 against thefilter housing 10 with the filter element 1 therebetween. A slipping ofthe locking element 22 on the filter housing 10 is prevented by allowingthe locking element to engage behind the respective protrusion 7 and tohold the grip. Thus, the respective protrusion 7, which is provided atthe filter element 1, allows in cooperation with the openings 12, thatthe secondary housing 20 can be clamped to the filter housing 10 bymeans of the locking elements 22. If third-party filter elements 1 areused, which do not feature the protrusions 7 or have them at anotherposition, the locking elements 22 slip off the filter housing, and thepermanent connection of secondary housing 20 and filter housing 10 isprevented. As a result, the improper use of inappropriate filterelements 1 can be prevented.

Furthermore, in FIG. 5 is illustrated that two blades 37 on the cyclonebottom section 33 besides the immersion tubes 36 towards the secondaryhousing 20 extend into the direction of the filter element 1 into theinterior space. The blades 37 are designed such that, with suitablefilter elements 1, they engage exactly into the gaps in the filtermedium 2. Otherwise, an inappropriate filter element blocks the assemblyof the air filter 30. Due to the blades 37, the air exiting the cyclonescan be calmed down on its way to the filter element 1, so that ahomogeneous oncoming flow of the filter element can be achieved.

FIG. 6 shows a perspective view of the filter housing 10 with view intothe interior space. Inner ribs 16 are provided on the filter housing 10.These ribs 16 extend in the installation direction of the filter element1 and reach the inside of the interior space. An accommodated filterelement 1 extends then by abutting on the ribs 16. The ribs 16 reproducea cross-sectional contour of the respective filter element to beinserted. Using the ribs 16 avoids using a filter element with a shapeother than for the intended use. This will ensure that the inflow spacecan be kept in the preferred size when using replacement filterelements. The ribs 16 can furthermore serve to homogenize the flow onthe outflow side of the filter element and in this case they can inparticular advantageously interact with with the blades 37.

FIG. 7 illustrates the filter housing 10 in top view, and FIG. 8 anappropriate filter element 1, which is inserted into the filter housing10. The ribs 16 and the shape of the filter element 1 with its filtermedium 2 are adapted to each other in such a way that exclusivelyprovided filter elements can be completely accommodated in the filterhousing 10 as a type of a key-lock principle. Furthermore, the top viewshows that the further protrusion 17 will not be blocked by a blockingelement 27 (cf. FIG. 3), if the filter element 1 is correctly orientedin relation to the filter housing 10. In this case, the end disk 8 has ashape adapted to the sealing edge 40. In this way, a good seal seat isnecessarily achieved.

FIGS. 9 and 10 show a further example of an embodiment of the invention.In this case, FIGS. 9A and 10A correspond to the FIGS. 9 and 10,respectively, wherein however the secondary housing 20 designed ashousing cover is blanked out for an enhanced visibility. However, thefastening elements 22, designed here as clamping brackets made of wire,which are attached to the housing cover 20 and can be removed with it,are still visible.

The air filter 30 shown in FIGS. 9-10 comprises a filter housing 10 andfilter element 1. Air to be cleaned flows from the top to an inlet 3,flows through the round filter element 1 and exits from an outlet notshown here in the perspective-rear area on the rear front face of thehousing in cleaned condition.

The filter element 1 comprises a star-shaped folded, annular, inparticular circular ring-shaped closed filter bellows made of a filtermedium such as, for example, fleece or cellulose or a combinationthereof. It features at the top end a sealing, round end disk 8, whichsealingly closes a front face of the filter element and thus separatesthe raw side outside of the filter element from the clean side in thefilter element interior space. The end disk features several fasteningelements 7 in the shape of protrusions or buttstraps, which can be inparticular disposed as shown at an annular extension 150 of the enddisk, which is connected with the inner area of the end disk, whichencloses the frontal end of the filter element by means of star-shapeddisposed distance ribs or a distance ring. Openings or holes 12 aredisposed in the filter housing 10, into which can engage the protrusions7. Once the filter element is accommodated in the filter housing 10,that means if they are in FIG. 9-10 completely telescoped essentially inhorizontal direction, the protrusions 7 engage into the holes 12. Inthis case, the protrusions 7 in the area of the holes 12 are so longthat they protrude in the orientation of FIG. 1 in the picture to theright from the holes 12 of the filter housing 10. The openings 12 areprovided outside of the filter housing 10 and do not create an access tothe interior space of the air filter 30. In this case, the filterelement 1 is particularly disposed with its end disk 8 between thefilter housing 10 and the secondary housing 20 designed as housingcover.

Locking elements 22, which are attached to the secondary housing 20 inthe form of wire clamps in this example of an embodiment, can thenengage into the protrusions 7, in the engagement area 152, where theprotrusions 7 protrude from the filter housing 10, so that the filterelement 1 can then be clamped between the secondary housing 20 and thefilter housing 10. Several locking elements 22 and correspondingprotrusions 7 and openings 9 are preferably provided which arepreferably evenly distributed across the circumference of the end disk.A mounting of the housing cover 20 is therefore impossible withoutinstalled filter element 1, so that an operation of the device withouteffective filtration can be avoided. Preferably 2-6, particularlypreferred 3-5 locking elements 22 are provided.

The end disk 8 of the filter element 1 is disposed between the secondaryhousing 20 and the filter housing 10, wherein the end disk is clampedbetween the two components when the locking elements 22 engage behindthe protrusions 7. The protrusions 7 are provided for engaging throughthe openings 12 on the filter housing 10 and prevent a rotating movementof the filter element 1 in the filter housing 10 when they are in theengagement position. A rotation of the filter element in case ofvibration load can often happen during operation of the device. In thiscase, irregularities in the filter element, e.g. irregular loading orthe connection point of an annularly closed folded filter bellows whichis difficult to be locally flowed through due to changing flowconditions can result in a modification of the signal of the air-flowsensor that is not desired. As a result, a rotation of the filterelement in operation and thus an undesired modification of the air-flowmeter signal can be prevented by the described assembly. The FIGS. 9-10show the assembly according to the intended use of the filter element 1and the housing components 10, 20. The locking elements 22 attached tothe secondary housing 20, which are realized in this example of anembodiment as wire clamp or bracket, clamp the secondary housing 20designed as housing cover against the filter housing 10 with the filterelement 1 therebetween. A slipping of the locking element 22 on thefilter housing 10 is prevented by allowing the locking element to engagebehind the respective protrusion 7 and to hold the grip. Thus, therespective protrusion 7, which is provided at the filter element 1, inparticular at its end disk 8, allows in cooperation with the openings12, that the secondary housing 20 can be clamped to the filter housing10 by means of the locking elements 22.

Although the present invention has been described above by means ofpreferred examples of an embodiment, it is not limited thereto, but itcan be modified in various ways. In particular, filter element andhousing can also be adapted to other filter types than cyclone filtersor equipment. It is also conceivable to provide three or more than fourbuttstraps for clamping the housing components.

The invention claimed is:
 1. An air filter system (30) for the intakeair of internal combustion engines, comprising: a filter housing (10);an annular filter element (1) replaceably received into a chamber withinthe filter housing; a secondary housing (20) secured to and closing thefilter housing (10) such that the secondary housing and filter housingenclosed the filter element in the chamber therein, the secondaryhousing including: at least one locking element (22) operable to engagethe filter housing and the filter element to lock the housing closed andlock the filter element therein; wherein the filter housing (10) isdesigned to internally accommodate and lock the filter element (1)therein; wherein the filter element (1) includes an end disk (8) securedonto an axial end face of the filter element (1), the end disk sealinglyclosing the axial end face separating a raw side from a clean side ofthe filter element; at least one fastening element (7), each embodied asan elongated axial protrusion (7) having a first end arranged at andsecured onto a radially outer portion of the end disk (8), the elongatedaxial protrusion (7) elongated in an axial direction extending axiallyaway from the end disk (8); wherein the filter housing (10) on itsexterior forms a least one receptacle (12) arranged on the exterior ofthe filter housing and having an axially extending hole (12) extendingthrough the receptacle and opening at opposing axial sides of thereceptacle; wherein the protrusion (7) extends axially from the filterelement end disk and completely through the hole and continues outwardlybeyond the hole when the filter element (1) is assembled with the filterhousing (10) in such a way that the filter element (1) is accommodatedin the filter housing (10); wherein a portion of the axial protrusionthat continues outwardly beyond the hole has a locking surface; whereinthe at least one locking element (22) of the secondary housing (20)engages the at least one fastening element (7) in such a way, when thefilter element (1) is accommodated in the filter housing (10) and isdisposed between the filter housing (10) and the secondary housing (20),that the secondary housing (20) is detachably clamped to the filterhousing (10).
 2. The air filter system (30) according to claim 1,wherein the filter element include a sealing element secured thereto andhaving a sealing element surface corresponding to a complimentarysealing surface of the filter housing (10); wherein the sealing elementis sealingly pressed against by press-fitted onto the correspondingsealing surface of the filter housing (10) when the secondary housing(20) is clamped to the filter housing (10).
 3. The air filter system(30) according to claim 1, wherein the at least one locking element (22)on the secondary housing (20) are pivotally mounted to the secondaryhousing, each of the at least one locking element operable to lock ontothe locking surface of a respective one of the at least one fasteningelement (7).
 4. The air filter system (30) according to claim 3, whereinthe at least one locking element (22) has a hook-shaped end, thehook-shaped end engaging against a respective one of the at least onefastening element (7) and behind the respective one of the at least onefastening element (7) or into a recess or undercut provided at or on therespective one of the at least one fastening element (7).
 5. The airfilter system (30) according to claim 4, wherein the at least onelocking element (22) on the secondary housing (20) is embodied as aresilient metal clamp.
 6. The air filter system (30) according to claim1, wherein the hole of the at least one receptacle (12) on the filterhousing (10) is disposed on the outer side of the filter housing facingaway from the filter element (1) on inclined filter housing sectionswhich extend under an angle between 45 and 90 degrees in relation to alongitudinal extension direction of the at least one receptacle hole(12).
 7. The air filter system (30) according to claim 1, wherein the atleast one fastening element (7) is at least four fastening elements (7);wherein the filter housing (10), the filter element (1) and thesecondary housing (20) are secured together by the at least fourfastening elements (7).
 8. A filter element (1) of the filter system(30) according to claim 1, the filter element comprising: an annularlyclosed filter medium (2); an end disk secured to the filter medium; atleast one fastening element (7), each embodied as an elongated axialprotrusion (7) having a first end arranged at and secured onto aradially outer portion of the end disk (8), the elongated axialprotrusion (7) elongated in an axial direction extending axially awayfrom the end disk (8); wherein when the filter element (1) isaccommodated in the filter housing (10) and disposed between the filterhousing (10) and the secondary housing (20), a respective one of the atleast one locking element (22) of the secondary housing (20) engageswith the at least one fastening element (7) such that the secondaryhousing (20) is clamped onto the filter housing (10).
 9. The filterelement (1) according to claim 8, wherein the at least one fasteningelement (7) axial protrusion extends through and engages into arespective hole (12) provided on the on the filter housing (10).
 10. Thefilter element (1) according to claim 9, wherein the filter element (1)includes an end disk secured on an axial end of the filter element (1)and sealingly closing the end face of the filter element to separate araw side from a clean side of the filter medium; wherein the axialprotrusion engages into a recess on the filter housing (10) or into therespective hole (12).
 11. The filter element according to claim 10,wherein the protrusion extends axially from an end disk of the filterelement (1) in a mounting direction of the filter element (1) into thefilter housing (10).
 12. The filter element according to claim 11,further including a circumferential a sealing element embodied as a sealring, sealing the filter element and separating a raw side from a cleanside in the filter housing (10); wherein the sealing element is arrangedon and secured to the end disk (8).
 13. The filter element according toclaim 12, wherein the axial protrusion (7) is arranged at an exterior ofthe filter housing, spaced outwardly from the sealing element andoutside of space enclosed by the filter housing (10) in which the filterelement (1) is received.